Washing machines commonly operate on a cyclical programme basis. For example, a typical wash will comprise a wash cycle, a rinse cycle and a spin cycle when the clothes are respectively, washed, rinsed and spin dried. There is normally a draining of liquor between these respective cycles. It is known to provide a pre-wash cycle before the main wash cycle, when it is desired to clean heavily soiled items. Again, there is normally a draining of the pre-wash liquor before dosing of the main wash liquor and execution of the wash cycle.
In the pre-wash, normally the same laundry cleaning product is used as in the main wash. However, it is also known to provide pre-wash compositions to be used in the pre-wash cycle alone, or in combination with some of the main wash composition. These pre-wash products or additives are often formulated so as to attack particularly difficult kinds of soil. When a pre-wash cycle is not used, tough stains may be pre-treated by for example applying undiluted detergent composition to the stained area before laundry is washed in the main wash-cycle. However, the use of a pre-wash cycle or pre-treatment costs extra time and energy. Therefore, there is still a need for an energy efficient laundry cleaning method which optimises the cleaning ability of cost-effective cleaning products.
WO-03/080916 discloses a washing method in a washing machine, wherein laundry is soaked effectively and conveniently. The washing method described in this document includes the steps of (1) loading laundry into the tub of the washing machine, (2) supplying the tub with washing water such that the water level increases step by step and (3) repeatedly soaking the laundry. Furthermore, U.S. Pat. No. 4,555,019 discloses a method of washing a laundry fabric in a wash liquor in a washing machine, wherein first a concentrated aqueous wash liquor is distributed onto the laundry, and subsequently rinse liquor (i.e. fresh water) is added. It can be noticed that in both of these prior art methods, the concentration of detergent material in the washing water within the tub is reduced significantly.
On the other hand, US-2003/0182732 discloses a portable, self-contained device for dosing and/or dispensing a detergent composition into an appliance for treating fabric. Furthermore, JP-6 079092 and JP-5 123489 disclose methods for refining water using electrolysis. In addition U.S. Pat. No. 5,965,505 can be mentioned which document discloses a detergent composition containing a heavy metal ion sequestrant and an organic peroxyacid bleaching system, whereby means is provided for delaying the release to a wash system of said bleach system.
We have now discovered that in a single wash cycle, a change in the wash liquor content can optimise the cleaning ability of the wash liquor.
The present invention resides in changing the ionic strength of the wash liquor during the wash cycle, whereby the concentration of surfactant material in the wash liquor is kept substantially constant during the wash cycle.
Although not wishing to be bound by theory, it is hypothesised that this influences the interaction between the stain and the surfactant (or a mixture thereof) enabling the removal of a wider variety of stains.